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We present a new set of reference materials, the ND70‐series, for
in situ measurement of volatile elements (H2O, CO2, S, Cl, F) in silicate glass of basaltic composition. The materials were synthesised in piston cylinders at pressures of 1 to 1.5 GPa under volatile‐undersaturated conditions. They span mass fractions from 0 to 6%m/m H2O, from 0 to 1.6%m/m CO2and from 0 to 1%m/m S, Cl and F. The materials were characterised by elastic recoil detection analysis for H2O, by nuclear reaction analysis for CO2, by elemental analyser for CO2, by Fourier transform infrared spectroscopy for H2O and CO2, by secondary ion mass spectrometry for H2O, CO2, S, Cl and F, and by electron probe microanalysis for CO2, S, Cl and major elements. Comparison between expected and measured volatile amounts across techniques and institutions is excellent. It was found however that SIMS measurements of CO2mass fractions using either Cs+or O−primary beams are strongly affected by the glass H2O content. Reference materials have been made available to users at ion probe facilities in the US, Europe and Japan. Remaining reference materials are preserved at the Smithsonian National Museum of Natural History where they are freely available on loan to any researcher.Free, publicly-accessible full text available July 25, 2025 -
Abstract The mainly deep-submarine Ontong Java Plateau (OJP) is the result of the largest outpouring of lava in the geologic record. Volcanic events of this magnitude can have dramatic environmental impacts due to volatile emissions. We report new S measurements in naturally glassy, olivine-hosted melt inclusions and pillow basalt glasses from the OJP. We combined these data with previous S measurements in OJP glasses to quantify S degassing in a suite of OJP glasses. Comparison with an S degassing model suggests OJP lavas that erupted at depths ~>1500 m did not degas S; OJP lavas that erupted at depths ~<1500 m degassed up to ~40% initial S, but these lavas likely made up a small fraction of OJP lavas. This result suggests that despite its large volume compared to continental large igneous provinces (LIPs), OJP lavas emitted less S, potentially contributing to its muted environmental impact. The OJP may provide a framework for the temporal evolution of S degassing at oceanic LIPs, with early eruptions at great water depths releasing limited to no S, and later eruptions at shallow water depths releasing larger, but still limited amounts of S. This framework may also have implications for continental LIP magmas, which may release significant amounts of CO2 but limited amounts of S during intrusive activity, with magmatic S emissions only becoming important during extrusive phases.
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Many problems in programming language theory and formal methods are undecidable, so they cannot be solved precisely. Practical techniques for dealing with undecidable problems are often based on decidable approximations. Undecidability implies that those approximations are always imprecise. Typically, practitioners use heuristics and
ad hoc reasoning to identify imprecision issues and improve approximations, but there is a lack of computability-theoretic foundations about whether those efforts can succeed.This paper shows a surprising interplay between undecidability and decidable approximations: there exists a class of undecidable problems, such that it is computable to transform any decidable approximation to a witness input demonstrating its imprecision. We call those undecidable problems
witnessable problems . For example, if a program propertyP is witnessable, then there exists a computable functionf P , such thatf P takes as input the code of any program analyzer targetingP and produces an input programw on which the program analyzer is imprecise. An even more surprising fact is that the class of witnessable problems includes almost all undecidable problems in programming language theory and formal methods. Specifically, we prove the diagonal halting problemK is witnessable, and the class of witnessable problems is closed under complements and many-one reductions. In particular, all “non-trivial semantic properties of programs” mentioned in Rice’s theorem are witnessable. We also explicitly construct a problem in the non-witnessable (and undecidable) class and show that both classes have cardinality 2ℵ0.Our results offer a new perspective on the understanding of undecidability: for witnessable problems, although it is impossible to solve them precisely, it is always possible to improve any decidable approximation to make it closer to the precise solution. This fact formally demonstrates that research efforts on such approximations are promising and shows there exist universal ways to identify precision issues of program analyzers, program verifiers, SMT solvers, etc., because their essences are decidable approximations of witnessable problems.
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Abstract The degassing of CO2and S from arc volcanoes is fundamentally important to global climate, eruption forecasting, ore deposits, and the cycling of volatiles through subduction zones. However, all existing thermodynamic/empirical models have difficulties reproducing CO2‐H2O‐S trends observed in melt inclusions and provide widely conflicting results regarding the relationships between pressure and CO2/SO2in the vapor. In this study, we develop an open‐source degassing model, Sulfur_X, to track the evolution of S, CO2, H2O, and redox states in melt and vapor in ascending mafic‐intermediate magma. Sulfur_X describes sulfur degassing by parameterizing experimentally derived sulfur partition coefficients for two equilibria: RxnI. FeS (
m ) + H2O (v )H2S ( v ) + FeO (m), and RxnII. CaSO4(m)SO2( v ) + O2(v ) + CaO (m), based on the sulfur speciation in the melt (m ) and co‐existing vapor (v ). Sulfur_X is also the first to track the evolution off O2and sulfur and iron redox states accurately in the system using electron balance and equilibrium calculations. Our results show that a typical H2O‐rich (4.5 wt.%) arc magma with high initial S6+/ΣS ratio (>0.5) will degas much more (∼2/3) of its initial sulfur at high pressures (>200 MPa) than H2O‐poor ocean island basalts with low initial S6+/ΣS ratio (<0.1), which will degas very little sulfur until shallow pressures (<50 MPa). The pressure‐S relationship in the melt predicted by Sulfur_X provides new insights into interpreting the CO2/STratio measured in high‐T volcanic gases in the run‐up to the eruption. -
Abstract Selection for yellow- and white-grain types has been central to postdomestication improvement of maize. While genetic control of carotenoid biosynthesis in endosperm is attributed primarily to the Yellow1 (Y1) phytoene synthase gene, less is known about the role of the dominant white endosperm factor White Cap (Wc). We show that the Wc locus contains multiple, tandem copies of a Carotenoid cleavage dioxygenase 1 (Ccd1) gene that encodes a carotenoid-degrading enzyme. A survey of 111 maize inbreds and landraces, together with 22 teosinte accessions, reveals that Wc is exclusive to maize, where it is prevalent in white-grain (y1) varieties. Moreover, Ccd1 copy number varies extensively among Wc alleles (from 1 to 23 copies), and confers a proportional range of Ccd1 expression in diverse organs. We propose that this dynamic source of quantitative variation in Ccd1 expression was created in maize shortly after domestication by a two-step, Tam3L transposon-mediated process. First, a chromosome segment containing Ccd1 and several nearby genes duplicated at a position 1.9 Mb proximal to the progenitor Ccd1r locus on chromosome 9. Second, a subsequent interaction of Tam3L transposons at the new locus created a 28-kb tandem duplication, setting up expansion of Ccd1 copy number by unequal crossing over. In this way, transposon-mediated variation in copy number at the Wc locus generated phenotypic variation that provided a foundation for breeding and selection of white-grain color in maize.more » « less